An increasing need to supply a growing world population with protein foods has led scientists to pursue many nonmeat protein sources. The protein contained in vegetable products, especially in oleaginous seed materials, is a valuable source of such protein for human consumption. The natural protein, however, is highly sensitive to the rigors of extraction and fractionation procedures and therefore the production of a highly nutritious and functional protein from oleaginous materials which can be converted into palatable meat-like food products has been a major obstacle to the general use of these materials. A great deal of research has been conducted to improve these extraction and fractionation procedures and various methods have been used.
Oleaginous seed materials are known to contain a large number of proteins, carbohydrates, salts and other cellular matter. It is from this complex mixture that proteins must be extracted and fractionated to produce useful food products. The extractability of oleaginous proteins from this mixture is greatly influenced by a variety of factors including temperature, pH, salt concentration and the like. For instance, the majority of the total proteins available in soybeans are largely insoluble in aqueous solution in the pH range from about 3.5 to about 6.0. The conventional extraction and fractionation procedure, utilizing this solubility phenomenon, produces protein isolates from defatted soybeans by solubilizing the protein in highly alkaline aqueous medium above pH 6.0, recovering the proteins by precipitation at their average isoelectric point, pH 4 to 5, and drying the precipitated proteins. These protein isolates are then useful as emulsifiers, binders and as the chief structural materials of meat analogs prepared by fiber spinning and heat gelation techniques. Although widely used for these purposes, the rigorous alkaline treatment frequently required to solubilize the proteins in the seed material or subsequently required to resolubilize and gel the proteins for fiber spinning or extrusion purposes results in some partial irreversible protein degradation and loss of physioelastic properties. In addition the proteins which are recovered by precipitation in acid salt solutions are invariably contaminated by large amounts of absorbed salts which are only partially removed by extensive washing.
It is therefore desirable to produce a highly functional and heat coagulable protein product which has not been conventionally treated under highly alkaline conditions and has not been contaminated with absorbed salts. A novel approach which solves some of the conventional problems is disclosed by Tombs in Great Britain Patent No. 1,265,661. Tombs avoids the need for highly alkaline pH conditions by preparing the plant proteins in the form of a mesophase, i.e., protein maintained in the dissolved state at a pH from 3 to 9 by a dissolved water-soluble salt. In this procedure, defatted oleaginous seed proteins are solubilized in an aqueous medium and precipitated at a pH of 4 to 6 to yield a protein isolate. A water soluble salt is then added to an aqueous suspension of the freshly separated protein isolate at a concentration based on a minimum ionic strength of 0.2 calculated on the water content of the composition. After centrifugation of this mixture, a dense phase of fluid aqueous protein or mesophase separates. This mesophase has the unique properties of fluidity and high dissolved protein concentration at a pH below that at which protein degradation occurs. Without further treatment the mesophase may be used in the preparation of spun fibers or used as a heatsetting binder for other edible materials. Unfortunately this procedure also recovers a protein which is contaminated with relatively high concentration of salts without which a mesophase having these unique properties could not be formed.